International Patent Publication No. WO0037904 discloses a conventional LED luminaire. The LED luminaire includes a circuit board mounting thereon plural kinds of LEDs of different colors (e.g., a red LED, a green LED, and a blue LED), a main body carrying the circuit board, and an optical member covering surfaces of the LEDs. In order to obtain a light of a desired chromaticity (e.g., white light), the LED luminaire further includes a single photodiode for detecting light outputs from all of the LEDs and a controller for performing a feedback control of regulating an amount of forward electric current to each LED in order to keep the light from the individual LED at a predetermined desired level. However, since the emitted light from each of LEDs is transmitted to the photodiode through an optical fiber, the LED luminaire has one disadvantage that it is difficult to detect light stably from all of the LEDs. Furthermore, since the control unit drives the red, green, and blue LEDs individually at short intervals and determines a light output level for each color, the LED luminaire has another disadvantage that it is difficult to adjust the chromaticity based upon the light of the mixed-color obtained from these LEDs, i.e., the light practically emitted from the LED luminaire.